Reduction of watermarks in HF treatments of semiconducting substrates

Abstract

A process for reducing or suppressing the appearance of watermarks in a hydrophobic surface of a semiconductor substrate prepared as a base substrate for epitaxial growth. The process includes cleaning the hydrophobic surface of the semiconductor substrate with an aqueous solution containing hydrofluoric acid (HF) and an additional acid having a pKa of less than 3, preferably hydrochloric acid (HCl), wherein the additional acid is present in the solution at a concentration by weight that is less than that of the HF; and final rinsing the cleaned hydrophobic surface of the semiconductor substrate with deionised water while subjecting the hydrophobic surface of the semiconductor substrate to megasonic waves for a time sufficient to reduce or suppress watermarks that could otherwise occur on the hydrophobic surface if the megasonic waves were not applied.

1. A process for reducing or suppressing the appearance of watermarks in a hydrophobic surface of a semiconductor substrate prepared as a base substrate for epitaxial growth, which process comprises:
 cleaning the hydrophobic surface of the semiconductor substrate with an aqueous solution containing hydrofluoric acid (HF) and an additional acid having a pKa of less than 3, wherein the additional acid is present in the solution at a concentration by weight that is less than that of the HF; and 
 final rinsing the cleaned hydrophobic surface of the semiconductor substrate with deionised water while subjecting the hydrophobic surface of the semiconductor substrate to megasonic waves for a time sufficient to reduce or suppress watermarks that could otherwise occur on the hydrophobic surface if the megasonic waves were not applied. 
 
     
     
       2. The process of  claim 1 , which further comprises conducting an additional rinsing with deionised water without the application of megasonic waves immediately after the cleaning and prior to the final rinsing. 
     
     
       3. The process of  claim 1 , which further comprises drying the substrate after the final rinsing. 
     
     
       4. The process of  claim 1 , wherein the megasonic waves are applied at a power in the range of at least 100 Watts and at most 1200 Watts, at a frequency of at least 1 kHz and at most 10 MHz and for a time in the range of at least 1 second and at most 5 minutes. 
     
     
       5. The process of  claim 1 , wherein the megasonic waves are applied at a power in the range of at least 800 Watts and at most 1000 Watts, at a frequency in the range of at least 700 kHz and at most 1 MHz, and for a time in the range of at least 10 seconds and at most 60 seconds. 
     
     
       6. The process of  claim 1 , wherein HF is present in the solution at a concentration in the range of 0.05% <[HF] by weight<49%. 
     
     
       7. The process of  claim 1 , wherein HF is present in the solution at a concentration in the range of 0.5% <[HF] by weight<10%. 
     
     
       8. The process of  claim 1 , wherein the additional acid has a pKa of less than 0 and the cleaning removes surface oxides and provides a hydrophobic surface for epitaxial growth. 
     
     
       9. The process of  claim 8 , wherein the additional acid is selected from the group consisting of hydrochloric acid (HCl), nitric acid (HNO3), sulphuric acid (H2SO4) and perchloric acid (HClO4). 
     
     
       10. The process of  claim 8 , wherein the additional acid is hydrochloric acid (HCl) and is present at a concentration in the range of 0.01% <[HCl] by weight<38%. 
     
     
       11. The process of  claim 8 , wherein the additional acid is hydrochloric acid (HCl) and is present at a concentration in the range of 0.01% <[HCl] by weight<5%. 
     
     
       12. The process of  claim 1 , wherein the hydrophobic surface is of the substrate is provided by a layer of silicon, strained silicon or silicon-germanium. 
     
     
       13. The process of  claim 1 , wherein the hydrophobic surface is of the substrate is provided by a layer of silicon-germanium. 
     
     
       14. The process of  claim 1 , wherein the cleaning is carried out in a single wafer cleaning device and is directly followed by the final rinsing. 
     
     
       15. The process of  claim 1 , which further comprises carrying out epitaxial growth on the cleaned and prepared hydrophobic surface of the semiconductor substrate. 
     
     
       16. The process of  claim 15 , wherein the hydrophobic surface of the substrate is provided by a layer of silicon-germanium (SiGe) layer or a strained silicon (sSi) layer. 
     
     
       17. The process of  claim 15 , wherein the hydrophobic surface of the substrate is provided by a layer of silicon-germanium (SiGe) layer having a germanium concentration of at least 20%, expressed as a percentage of Ge atoms with respect to Si atoms, at the surface of the substrate. 
     
     
       18. The process of  claim 15 , wherein the epitaxial growth comprises growth of a strained silicon (sSi) layer or a silicon-germanium (SiGe) layer on the hydrophobic surface of the semiconductor substrate. 
     
     
       19. A process for reducing or suppressing the appearance of watermarks in a hydrophobic surface of a semiconductor substrate prepared as a base substrate for epitaxial growth, which process comprises:
 cleaning the hydrophobic surface of the semiconductor substrate with an aqueous solution containing hydrofluoric acid (HF) and hydrochloric acid (HCl), wherein the HF is present in the solution at a concentration in the range of 0.5% <[HF] by weight<49% and the HCl is present at a concentration in the range of 0.01% <[HCl] by weight<38% with the HCl present in the solution at a concentration by weight that is less than that of the HF; and 
 final rinsing the cleaned hydrophobic surface of the semiconductor substrate with deionised water while subjecting the hydrophobic surface of the semiconductor substrate to megasonic waves for a time sufficient to reduce or suppress watermarks that could otherwise occur on the hydrophobic surface if the megasonic waves were not applied; 
 wherein the megasonic waves are applied at a power in the range of at least 100 Watts and at most 1200 Watts, at a frequency of at least 1 kHz and at most 10 MHz and for a time in the range of at least 1 second and at most 5 minutes. 
 
     
     
       20. The process of  claim 19  wherein the HF is present in the solution at a concentration in the range of 0.5% <[HF] by weight<10% and the HCl is present at a concentration in the range of 0.01% <[HCl] by weight<5%, and wherein the megasonic waves are applied at a power in the range of at least 800 Watts and at most 1000 Watts, at a frequency in the range of at least 700 kHz and at most 1 MHz, and for a time in the range of at least 10 seconds and at most 60 seconds.